The dual roles of melatonin biosynthesis enzymes in the coordination of melatonin biosynthesis and autophagy in cassava

Abstract

Both autophagy and melatonin play important roles in plant development and stress response. However, the direct correlation between autophagy and melatonin as well as the underlying mechanism remains elusive in plants. In this study, we discovered that the expression of three autophagy‐associated genes (MeATG8b, 8c, and 8e) and autophagic activity were induced by exogenous melatonin treatment in cassava. In addition, three melatonin biosynthesis enzymes (tryptophan decarboxylase 2 (MeTDC2), N‐aceylserotonin O‐methyltransferase 2 (MeASMT2), and MeASMT3) positively regulate endogenous melatonin level and autophagic activity. Further investigation showed that these melatonin biosynthesis enzymes interacted with MeATG8b/8c/8e in vivo and in vitro. Consistently, MeTDC2, MeASMT2, and MeASMT3 also positively regulate endogenous melatonin level and autophagic activity in cassava. Notably, overexpression of MeATG8b, 8c, and 8e facilitated the protein expression level of MeTDC2, MeASMT2, and MeASMT3 in vivo. Taken together, melatonin synthesis enzymes (MeTDC2, MeASMT2/3) interact with MeATG8b/8c/8e and thus coordinate the dynamics of melatonin biosynthesis and autophagic activity in cassava, highlighting the links between melatonin biosynthesis and autophagic activity in cassava.

Melatonin: A master regulator of plant development and stress responses

“…Autophagy, a process that helps maintain cellular homeostasis by degrading and recycling cytoplasmic materials, is a highly conserved, tightly regulated pathway in eukaryotes (Qi et al, 2020). This central pathway is required for plant development and stress responses in plant cells (Qi et al, 2020;Wei et al, 2020). However, in all cases, autophagy is related to oxidative stress in both plants and animals (Qi et al, 2020;Wei et al, 2020).…”

“…This central pathway is required for plant development and stress responses in plant cells (Qi et al, 2020;Wei et al, 2020). However, in all cases, autophagy is related to oxidative stress in both plants and animals (Qi et al, 2020;Wei et al, 2020). There is increasing evidence that melatonin has beneficial effects on the regulation and restoration of damaged autophagic processes in plants.…”

“…Melatonin-mediated activation of autophagy might be part of a survival mechanism in response to cellular damage. During this process, melatonin biosynthesis enzymes including TDC and ASMT interact with autophagy-associated genes, coordinating the dynamics of melatonin biosynthesis and autophagic activity in cassava (Manihot esculenta; Wei et al, 2020). Thus far, the direct link between autophagy and melatonin in plants and the underlying mechanism remain elusive.…”

“…It is becoming clear that melatonin and auxin signals are transmitted via different signaling cascades, which ultimately converge at some (not necessarily regulatory) checkpoints. The signaling molecule nitric oxide (NO), which plays myriad roles in modulating growth and development as well as in environmental interactions in plants (Stöhr and Stremlau, 2006; Wilson et al, 2008; Sun et al, 2014; Yu et al, 2014; Sanz et al, 2015), is emerging as a pivotal player in melatonin and auxin signaling. NO regulates auxin responses, resulting in adventitious root formation and functioning in lateral roots and root hair development as well as root gravitropism (Pagnussat et al, 2002; Yu et al, 2014).…”

Melatonin Regulates Chloroplast Protein Quality Control via a Mitogen-Activated Protein Kinase Signaling Pathway

“…The representative roles of melatonin in plant growth and development include promoting seedling growth [13], early flowering [21,22], enhanced seed germination and viability [23,24], delayed senescence [25], diurnal stomatal closure [26], and increased secondary metabolites [27], etc. [20,28,29]. Moreover, melatonin has a profound effect on plant defenses against a vast array of adverse environmental stresses, helping plants to survive and thrive [30].…”